AFter uninstalling Avira using the standard method from Add/Remove Programs, then download and run the Avira Registry Cleaner from the link below. It helps clean out any registry remnants of the old version of Avira. You'll need to unzip the registry cleaner before running it.
Here's the link for the new version download:
I am running Avira Anti-Virus and tried to upgrade and now when I reboot a get a message CCPLG.XML unable to find file C:\Program Files\Avira\AntiVir Personal Edition Classic\ccplg.xml. When I pull up Windows security it shows that I have anti-virus protection however I can't run a scan or access the program without getting this message.